This invention especially relates to the regeneration of caustic impregnated activated carbon by a three stage process, involving the use of both a high concentration (30 to 50 percent) and then a low concentration (5 to 25 percent) NaOH or KOH solution.
Activated carbons impregnated with NaOH have been described in U.S. Pat. No. 4,072,479 to Sinha et al. and it is my intent to incorporate by reference the contents of the Sinha et al. patent.
Activated carbons impregnated with KOH have been described in G.B. Pat. No. 1,394,031 to Cooley et al. and in Swinarski et al. Chem. Stosowana, Ser. A 9(3), 287-94 (1965), (Chemical Abstracts, Vol. 64, 1379c).
Caustic impregnated carbons are excellent adsorbents for malodorous sulfur and organic compounds. As used herein, caustic impregnated carbon refers to carbon impregnated with either NaOH or KOH. Caustic, therefore, is defined as NaOH or KOH and may also include any other alkali metal hydroxide. Typical malodorous sulfur containing compounds include principally hydrogen sulfide, mercaptans and sulfides. The malodorous organic compounds include all of those compounds formed by the bacterial breakdown of higher organic compounds, for example, compounds associated with sewer treatment facilities.
Adsorption of such malodorous compounds reduces the effective capacity of the carbon for further adsorption. At some point in time (known as the breakthrough), the carbon becomes spent, that is, it looses its capacity to adsorb. At that point, the carbon must be regenerated.
Prior to the discovery of the three step regeneration process of the present invention, carbons of the type described by Sinha et al. were regenerated by treatment of the spent carbon with a 50 percent NaOH solution for at least 18 hours, followed by one water rinse.
By using the process of the present invention, a high concentration caustic wash followed by a low concentration caustic wash, or vice versa, improved regeneration of adsorptive capacity of from 10 to 20 percent over the processes of the prior art is achieved.